This invention relates generally to arrangements and methods for determining the level of particulate contaminants in fluids in a fluid system, and more particularly, to a system whereby the fluid is passed through a filter medium having a substantially predetermined pore size; the contamination level being determined by measuring the volume of fluid passing through the filter medium prior to the blockage thereof causing a reduction of fluid flow therethrough to a predetermined level.
In fluid systems, particularly tribological systems such as hydraulic, lubricating, fuel, and many process systems, it is essential to detect and measure the concentration of particulate contaminants entrained in the fluids. It is well known that high levels of such contamination will dramatically decrease the efficiency and life of machinery associated with such fluids.
The most common technique for measuring the contamination levels of fluids requires microscopic or photoelectric counting. The systems required for performing such counting are generally not portable or too delicate for field use, thereby requiring a laboratory environment for their use. Some of the currently known methods which are used to quantify the concentration of particles in a fluid employ gravimetric and volumetric techniques, so as to assess the silting effects of particulate contamination in the fluids. ASTM F52-65T cites an apparatus which is useful in obtaining the silting index.
A further known approach to obtaining of a measure of the contamination of a fluid utilizes a photoelectric system which generates a form of light which is passed through the fluid and detected by a photodetector. The level of contamination of the fluid is inversely related to the intensity of the light which reaches the photodetector. It is a problem with such light-dependent contamination sensors that they are too delicate for installation directly on machines which are subject to vibration and shock, and which are exposed to hostile environmental conditions. Additionally, the calibration of such sensors for each type of fluid and for the various types of entrained contaminants requires extensive on-site or on-board instrumentation which substantially increases the cost of such a system beyond what can be justified for the fluid systems.
The silting index method of determining the degree of contamination is essentially a laboratory-oriented technique which provides a semiquantitative assessment of particulate contamination in the silt size range of between approximately 0.5 to 5.0 micrometers. In essence, this known method measures the decay in the rate of fluid flow resulting from the clogging of a membrane when a contaminated fluid sample is passed therethrough. Particles having a size greater than the pore size of the membrane are retained by the filter medium membrane. It is a problem with the method that it is characterized by poor repeatability because particles which are much greater in size than the silt sized pores of the membrane form a loose, open filter cake, while particles having a smaller size than the pore size, or stable gels resulting from oxidation products and polymers, tend to block the pores of the membrane in an unpredictable manner.
A further known system for determining the level of contamination in a fluid utilizes the passing of the system fluid through a filter medium until a predetermined pressure drop is achieved across the filter medium. The level of contamination in the fluid is determined by measuring the time required to reach the predetermined pressure level. This method, therefore, has several problems. First, the known method is sensitive to the pressure level of the system upstream of the sensing filter medium, thereby requiring the use of an auxiliary pump to circulate a stream of the fluid at a constant pressure. This known system, therefore, produces a contamination indication which is subject to the effects of system flow rate, system pressure differential, and fluid viscosity. Correction of the results produced by this system to compensate for such effects would require substantial additional cost.
It is, therefore, an object of this invention to provide a fluid contamination monitoring system which is simple and inexpensive.
It is another object of this invention to provide a fluid contamination measurement system which is easily portable and rugged enough for field use.
It is also an object of this invention to provide a contamination level analyzer and monitor system which can be integrated as part of a fluid system.
It is additionally an object of this invention to provide a fluid contamination level analyzer and monitor system which can provide continuous evaluation of the fluid.
It is also an object of this invention to provide a fluid contamination analyzer and monitor which is resistant to the adverse effects of the contaminant in the fluid.
It is another object of this invention to provide a contamination level monitoring device which is insensitive to fluctuations in the rate of fluid flow.
It is a still further object of this invention to provide a system for measuring the contamination level of a fluid and which is insensitive to fluctuations in the fluid pressure.
It is still another object of this invention to provide a system for determining the level of contamination in a fluid which is insensitive to temperature variations of the fluid and the ambiance.
It is yet another object of this invention to provide a fluid contamination measuring system which is insensitive to the viscosity of the fluid.
Another object of this invention is to provide a contamination monitoring system which discriminates between particles of different sizes.
A further object of this invention is to provide a contamination monitoring system which is responsive to the concentration of particles in a designated size range.
Another object of this invention is to provide repeatable and reliable fluid contamination measurements throughout a wide range of contamination levels.
A still further object of this invention is to provide a contamination measuring system which exposes the detection element to the fluid flowing within the system.
A yet further object of this invention is to provide a contamination measuring and analyzing system which utilizes a filter medium which can be rejuvenated by backflushing.
Still another object of this invention is to provide a contamination measuring system which samples the fluid in a fluid system automatically.
A yet further object of this invention is to provide a system for detecting the level of contamination of a fluid with respect to a predetermined range of particle sizes.
Still another object of this invention is to provide a particulate contamination monitoring system which can be simply and inexpensively adapted to various size ranges of particulate contaminants.